1. Field of the Invention
This invention relates to an optical image reading device, and more particularly to an optical image reading device for optically reading a symbol formed on an article.
2. Description of the Related Art
In supermarkets, article information such as article name and price is printed on labels and the labels are attached to respective articles. Recently, the article information has been represented not only by characters and numerals but also by bar code formats for simplification of the settlement service. In this case, when the customer comes to the counter with articles put in a basket, the cashier or operator takes out the articles one by one from the basket, placing each article so that the image reader can read the bar code thereof, and then puts the articles into another basket or a paper bag, for example. The image reader acts in place of the cashier to input or register article information derived from the readout bar code into the cash register. After the registration for all the articles is completed, the cash register issues a receipt based on the registered article information.
FIG. 1 schematically shows the construction of the conventional optical image reader for reading the bar code from the label of the article. In the image reader, light generated from light source 1 is guided to reading window 4 by means of optical guide 6 in cabinet 2 and is emitted via reading window 4 to a limited external space. When label 9 attached to article 8 is set to face reading window 4 and the light is reflected to window 4 by label 9, the reflected light is directed to detection circuit ID by means of optical guide 6. Detection circuit ID reads the bar code of label 9 from the incident light to detect article information represented by the readout bar code. Light source 1 is generally constituted by use of a helium-neon (He-Ne) gas laser tube in order to reliably detect the tone of the light corresponding to the bar code.
In general, it is known that the service life of the gas laser tube is about 10,000 hours. Therefore, if the image reader is used in a shop which is open for 24 hours a day, it becomes necessary to replace the gas laser tube once each year.
In order to lengthen the serviceable period of the gas laser tube, that is, the period from the beginning of the use of the tube until the replacement thereof, it is considered viable to turn off the gas laser tube based on the judgment of the operator in, for example, the late evening, during which time the number of customers is minimal, and turn it on when necessary. However, in this case, the job of the operator is added to the normal job to increase the load on the operator.
It is further considered viable to set, on cabinet 2, a photo switch which energizes the gas laser tube when detecting the article. However, this method limits the transfer passage of the article. That is, when the article is taken out from the basket and is set to face reading window 4 without passing the photo switch, the gas laser tube is not energized. In this case, it is necessary to move the article to a position near the photo switch and set it again to face reading window 4, thus delaying the service.